This invention relates to a variable electromechanical device, such as a rotary potentiometer, a rotary switch, or similar devices which are actuated by means of a rotary shaft.
To ensure safe and proper operation, the axial play of the shaft within the device housing should not be excessive. To meet with this requirement, it is known to cut an annular groove in the shaft and to provide a pin penetrating a wall of the housing and engaging the groove. It is furthermore known to secure shafts by retaining rings or discs disposed in annular grooves. Furthermore, axial movement of the shaft can be prevented by a wire clamp which extends through a wall of the housing and engages an annular groove provided at an according location of the actuation shaft. A further arrangement for preventing axial movement of the shaft relative to the housing is known, in which a thrust washer and a spacer disc are disposed between the housing and the flange of a threaded sleeve. The spacer disc has a sector-shaped recess in which a retainer is inserted. This retainer is held by bending a projecting portion of the thrust washer and engages an annular groove of the actuation shaft. The rather great number of individual parts renders this arrangement very complicated and expensive.
It is furthermore known to retain the actuation shaft in a potentiometer housing by providing on the housing four resilient detent noses which engage at least one annular groove of the actuation shaft without play. It is a disadvantage of this arrangement, however, that the detent noses, while resisting pressure on the shaft, may spread apart under tension and depending on the respective chamfering provided, so that the shaft is no securely retained. In the known arrangement, an extension is formed on the housing which serves as both a stop for the spring carrier of the potentiometer and a holder for the collector thereof.
A variable resistor is also known, in which an actuation shaft is rotatably mounted in a housing. A second shaft has a sleeve-shaped extension which is fit onto an end of the actuation shaft. A portion of the extension is pressed into an annular groove of the actuation shaft and bears against the wall of the groove. A flattening of the shaft at the end thereof forms a projection which bears against a projecting collar located in the bore of the sleeve-shaped extension. This achieves a retaining of the shaft against pressure and tension.
Furthermore, a method of forming a spindle resistor is known in which the spindle on which the spring carrier is mounted, is retained in a housing by means of ultrasonic welding. The spindle has a threaded shaft with a conical tip and an annular groove formed by projecting ribs. During production, one end of the spindle is pressed into the housing and fixed there by means of ultrasonic vibrations and axial pressure. Also by ultrasonic means, softened thermoplastic material of the housing flows into the annular groove, thereby forming a second bearing for the spindle. The spindle is thereby retained against pressure and tension.